What process describes the movement of molecules from areas of high concentration to low concentration?

The correct answer is diffusion, a fundamental process in biology. Diffusion is defined as the net movement of molecules from a region of higher concentration to a region of lower concentration, driven by the concentration gradient. This movement continues until the concentration is uniform throughout the space; this is known as achieving equilibrium.

Diffusion occurs naturally and does not require energy input, making it a passive transport mechanism. It is essential for various biological processes, such as gas exchange in the lungs and the transport of nutrients and waste products across cell membranes.

In contrast, active transport involves the movement of molecules against their concentration gradient, requiring energy input, often in the form of ATP. Facilitated diffusion also involves the movement of molecules down their concentration gradient but requires specific transport proteins to assist in the process. Endocytosis is a mechanism where cells internalize substances by engulfing them in a vesicle, a process that also requires energy and does not involve simple concentration gradients.

Understanding these concepts provides insight into how substances move within biological systems and how cells maintain homeostasis.